This invention relates to grinding machines, and more particularly to a grinding machine for generating end cutting teeth in end mill cutters by gashing.
An end mill cutter, which is often referred to simply as an end mill, is a metal cutting tool of cylindrical shape having cutting teeth along both its periphery and one of its ends. This renders the tool suitable for recess work as well as a wide variety of other milling operations.
To manufacture an end mill, cylindrical bar stock, which should be high speed tool steel, is milled along its cylindrical surface to provide flutes which extend all the way up to one of the end faces. Next the steel is hardened in a heat treatment process. Then the edges of the flutes are ground to establish the peripheral cutting edges.
To establish the cutting teeth at the end of the tool, the end face of the cylindrical bar is first dished about one to three degrees so that the center of its end face is slightly deeper than the periphery. Next it is ground in a gashing operation to provide gashes which open out of the dished end face and generally align with the flutes. The gashes in effect create end cutting teeth at the end of the tool, there being a separate tooth at the end of each flute. Then primary and secondary surfaces are ground into the end face between gashes in a facing operation to establish cutting edges with the back surfaces of the gashes and trailing clearances. Finally, radii are ground into the tool to merge the end cutting edges along the gashes and peripheral cutting edges along the flutes. Since the teeth at the end of the tool are generated on hardened tool steel, the dishing, gashing, facing and radiusing operations are all achieved by grinding with an abrasive wheel.
Moreover, dull or damaged end mills are reconditioned by cutting off their ends, regrinding their flutes, and then establishing a new set of end teeth by the foregoing dishing, gashing, facing and radiusing operations.
Most end mills are gashed on a universal tool grinders that are manually operated. As a consequence, the quality of the grind depends to a large measure on the skill and judgment of the operator, but even with skilled grinding machine operators, the finish grinds for the gashes vary from one end mill to another. Moreover, the grinding is tedious and time consuming work requiring the skills of experienced machine operators. Aside from that, the typical universal tool grinder has a relatively small grinding wheel and a low powered motor to drive it, and this necessitates frequent dressings of the wheel. This is likewise a manual operation which can affect the geometry of the gashes that are eventually cut. Furthermore, the grinding wheel of a universal tool grinder operates dry since the grinder does not accomodate a coolant system, and this can cause excessive temperatures and reduce the metal hardness along the cutting edges of the end mill--the very regions which should remain as hard as possible.